Preheat the oven to 400° F. Toss the eggplant, red and yellow bell peppers, onion and garlic with the olive oil, salt, and pepper on a large baking sheet. Roast for 20 minutes, until browned, turning once with a spatula.
Bring a large pot of water to a boil. Salt it generously. Cook the orzo according to instructions. Drain. Rinse. Transfer to a large mixing bowl and let it cool.
For the dressing, combine the lemon juice, olive oil, salt, and pepper and pour on the pasta and vegetables. Let cool to room temperature, then add the scallions, pignolis, feta, and basil. Check the seasonings, and serve cooled or at room temperature.